During the last 3 years there has been an important breakthrough in the application of high resolution NMR spectroscopy to the study of polynucleotide structures. In the present proposal we outline various ways in which high resolution NMR will be used to study the structures of RNA molecules in solution. One goal will be to determine the complete secondary and tertiary structure of selected RNA molecules, and a number of different approaches to this are outlined. Another objective will be to resolve important questions which arose in connection with our earlier studies of other tRNA molecules. A third aspect of this work will be to determine the secondary, and if possible, tertiary structures of 5S RNA from a variety of sources so that these may be compared with the structural data already obtained with E. coli 5S RNA. The susceptibility of the RNA structures to alteration by variation in the important solvent variables (pH, ionic strength and Mg ions) and the addition of selected drugs will be investigated. The significance of this work is several fold. First, we are developing NMR as a polynucleotide structural tool. Secondly, we have selected for study a set of tRNA molecules which have interesting, and unique properties. Finally, these studies should permit us to build up a set of "rules" whereby it will be possible to deduce the secondary and tertiary structure of any RNA molecule in solution simply from a knowledge of its primary structure.